'98 Limited 5.0 overheating mystery...Help, please...

[SootsMe]

Hi Folks,
I just bought this awesome rig that's in great shape, having had about $6,500 invested by the previous (2nd) owner. He had a pro pull the engine to fix a leaky main seal, and due to nearly 200k miles considered replacing the engine. However, upon examination the innards were amazingly clean and in excellent order. That said, the water pump, all the gaskets & seals and some other stuff were replaced anyway since they were already into it. Since then, prev owner drove it a bit last winter with no problems, then it mostly was parked for a few months. Enter Me...My Aerostar blew a head gasket and being very tired, I sent it to Ford heaven. My friend Dave then offered to trade me the Explorer for some work that he's too old to do himself. Cool... I drove it for a week or so, no problem- temp guage exactly centered in the Normal zone & computer message system saying "Engine temperature OK". I needed to go from Salt Lake City to Idaho, so my son & I took off one evening to make the trip. A ways North on the Interstate, the speed limit goes up to 80 and we were doing about 83 (with AC on) for a while then noticed the temp guage climbing, so slowed to about 65 and things went back to normal. got to our destination, concluded our business & headed back in the (cooler) morning, going between 70-75 not using AC. Checking electronic system status, still says Engine temp is OK. Since then, it's gotten progressively worse and now it's overheating even at 30-35 with no AC and now the monitor system says "Check Engine Temperature". Radiator, thermostat, & fan clutch have all been replaced with name brand new stuff, new high end coolant, and the problem persists. Using an infrared thermometer, the highest reading I can get is at the thermostat housing area, around 185-192. No oil in coolant or coolant in oil. I am at wit's end here. Any thoughts (and prayers) would be greatly appreciated...Thank you for your help.

 

[SootsMe]

SOLVED! Opened radiator cap & couldn't see any coolant. Topped it up, idled a bit, topped up, 4X, didn't actually take very much, but likely a factor... Also, the hose between the radiator & the reservoir tank was plugged with some sort of snotty stuff! That probably wasn't any help. Now it'll go fast or slow with or without AC & the guage stays just shy of 1/2 in the Normal band. I'm smiling.

 

[Turdle]

That's your issue.
The snotty stuff was allowing the expanding coolant in to the reservoir, but it wasn't letting it get back to the radiator, because the gunk gets collected in the little output nipple on the bottom of the reservoir. Keep an eye on this because chunks may return, they may be all over the cooling system inside the engine block. Over time, thy will build back up.

You might consider a complete flushing of the engine coolant, remove the radiator and back flush it while it is upside down, and, remove the reservoir so you can wash it out upside down also-

 

[koda2000]

That's your issue.
The snotty stuff was allowing the expanding coolant in to the reservoir, but it wasn't letting it get back to the radiator, because the gunk gets collected in the little output nipple on the bottom of the reservoir. Keep an eye on this because chunks may return, they may be all over the cooling system inside the engine block. Over time, thy will build back up.

You might consider a complete flushing of the engine coolant, remove the radiator and back flush it while it is upside down, and, remove the reservoir so you can wash it out upside down also-

This is good advice, but the other reason that the rad doesn't draw from the expansion tank may be that the radiator is leaking. This usually happens because the end-tank seals leak, If the leak is higher up on the rad it may not overheat, but when coolant should be going in/out of the expansion tank it either leaks or sucks air from the bad seal. You should never have to add coolant to the radiator directly. The solution is to replace the radiator.